Is there a true correlation between today’s digital noise to yesterday’s film grain? Absolutely. It all has to do with light, or the absence thereof.
In days of photographic film and silver halide, tonality was recorded by light hitting silver and changing its properties. When light hit film, the silver content of the film was “exposed.” Until this exposed film was bathed in developer fluid, no evidence of the change was evident. However, when developer did come in contact with the sensitized silver, each grain was “cooked,” so to say. The amount of time the film was left in contact with the developer fluid and the temperature of this fluid changed these transparent particles into “burned” particles. The longer the film was exposed to light, the more dense (and pronounced) it became.
There is a direct correlation between the film’s exposure and the developing solution’s influence on this silver. An image that was captured in a low-light situation required more exposure time to register properly on the silver halide particles. Images captured in abundant light require less time to properly expose. Sort of like filling a glass with water. Under a forceful stream of water a glass may fill up in a short amount of time. Turn the water volume down and the glass takes longer to fill.
However, there is a way to change this relationship between light brilliance and exposure time, but it comes with a tradeoff side-effect. If the image is captured in low lighting conditions with insufficient exposure time, the development process can be enhanced to accommodate the low exposure. One of two (or perhaps both) ways to increase the film’s silver density is to 1) heat-up the developing solution and thus have a more harsh scorching effect on the silver, or 2) increase the development time to more thoroughly darken all available exposed grains of silver. This is akin to exposing nice pink skin to harsh sunlight for an extended period of time. Either behavior yields the same result… scortch!
When underexposed and over-developed film is processed, the grains of silver become much more pronounced, as in “grainy.”
On the digital side of the fence, poorly exposed CCDs (charge coupled devices) lack enough light to register light energy. The CCDs in your camera are like little light meters… they simply record the amount of light present in a given area. We call these areas of digital film shadows. These shadow areas are dark by nature on the computer monitor because of a lack of light striking that part of the CCD array (this digital film behaves like its analog film counterpart).
When a dark portion of the digital image is lightened (using either the Levels or Lighten Shadows tools), there is often not enough “information” in the image to deliver meaningful tonal value. Instead, unevenly exposed pixels deliver a “noisy” result. Noise is nothing more than sketchy electronic information. When asked to produce meaningful detail, these underexposed light meters deliver sandpaper-type irregular pixels.
So what do we conclude? Low lighting causes pronounced and unattractive results from both analog film and digital cameras. In this way, digital noise and film graininess are quite similar results. The answer to the film problem was either more light in the scene or airbrushed prints. The answer for digital film is much more attractive… either more light (as with film), or shooting in RAW mode, capturing more information, or digital airbrushing using image editing software.
Herb
